How a Heart-Lung Machine's Stress Leaves a Chemical Trail
Imagine a surgeon stopping a human heart to repair it. For decades, this was the impossible dream of cardiac surgery. The invention of the heart-lung machine made it reality, taking over the vital work of the heart and lungs so surgeons could operate on a still, bloodless field. But early pioneers like Clarence Crafoord and Åke Senning faced a mystery: even when the surgery was a technical success, patients sometimes struggled to recover. The question was, why? The answer, it turned out, was written in the patients' blood, in the form of microscopic enzymes released by stressed and injured cells. This is the story of how scientists learned to read this chemical SOS, turning a simple blood test into a window for safeguarding the human heart.
Temporarily takes over the function of the heart and lungs during surgery
Chemical markers released when cells are damaged or stressed
To understand this story, we first need to know what enzymes are. Think of your body's cells as a bustling factory. Enzymes are the specialized workers and machines inside that factory, orchestrating every chemical reaction needed for life—from breaking down food for energy to building new proteins.
Normally, these "workers" stay inside their cellular "factories." But when a cell is damaged or dies, its contents spill out. This is especially true for muscle cells, which are packed with enzymes needed for their high-energy work. The heart is a powerful muscle, and when it's handled, stopped, and restarted during surgery, some cells inevitably become distressed.
Key Insight: By drawing blood and measuring the levels of these escaped enzymes, doctors can get a surprisingly detailed report card on what's happening inside the body. It's like listening to the sounds coming from a factory; silence is good, but the clatter of broken machinery spilling into the street tells you something has gone wrong.
Cells contain enzymes that facilitate chemical reactions
Damaged cells release enzymes into the bloodstream
Blood tests detect elevated enzyme levels
In the early days of open-heart surgery, a crucial study set out to map precisely how serum enzymes behaved in patients undergoing procedures with the Crafoord-Senning machine. The goal was to establish a "normal" pattern of injury, distinguishing it from dangerous complications.
A group of patients scheduled for elective open-heart surgery (like valve repairs) were selected. Their pre-operative health was well-documented.
Before any incision was made, a blood sample was taken from each patient to establish their normal, baseline enzyme levels.
The surgery proceeded using the Crafoord-Senning heart-lung machine, which took over circulation and oxygenation for a defined period.
After surgery, blood samples were drawn at strict intervals: immediately after surgery, 6 hours post-op, 24 hours post-op, and daily for the next 5-7 days.
Each blood sample was analyzed in a laboratory to measure the concentration of specific enzymes known to be relevant to heart and muscle damage.
The results painted a clear and dramatic picture. The data revealed a predictable pattern of enzyme release, a direct signature of the controlled injury sustained during surgery.
This chart shows a typical pattern for Creatine Kinase-MB (CK-MB), a very heart-specific enzyme. Its peak and decline are classic markers of surgical heart injury.
Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) are often associated with the liver. Their pattern reflects the body's systemic response to being on bypass.
Lactate Dehydrogenase (LDH) is found in many tissues. A high total LDH confirms widespread cellular stress, but its pattern helps differentiate its source.
| Time Point | Average Total LDH (Units/L) | Clinical Significance |
|---|---|---|
| Pre-Op (Baseline) | 150 | Within normal limits |
| 24 Hours Post-Op | 400 | Confirms significant cellular injury has occurred |
| Day 2-3 | 550 (Peak) | Reflects the cumulative stress on heart, blood cells, and other tissues |
| Day 7 | 300 | Slowly trending down as the body recovers |
Scientific Importance: This study was revolutionary because it quantified the expected. By defining the normal "envelope" of enzyme release for a successful surgery, doctors gained a powerful tool. If a patient's enzyme levels soared far beyond this expected pattern—for instance, if CK-MB levels were twice the norm—it was a red flag, suggesting a complication like a post-operative heart attack. This turned a vague feeling of a patient "not doing well" into an objective, measurable warning sign.
So, how do researchers actually measure these tiny chemical messengers? Here's a look at the essential "reagent solutions" and tools they use.
Sterile vacuum tubes used to collect and preserve blood samples without clotting.
A machine that spins blood samples at high speed to separate the red blood cells from the clear, yellow serum where the enzymes are dissolved.
The core detection device. It measures how much light a solution absorbs. Many enzyme tests create a colored product; more enzyme = more color = a higher reading.
Specific chemicals that the target enzyme (e.g., CK or AST) acts upon. Each enzyme test uses a unique substrate.
Helper molecules that are essential for the enzyme's reaction to proceed. Changes in these cofactors are often what the spectrophotometer detects.
Maintain the perfect pH and salt balance in the test tube, ensuring the enzymes work optimally during the measurement.
The study of serum enzymes during open-heart surgery was a paradigm shift. It moved patient care from a reactive stance—waiting for obvious physical symptoms of failure—to a proactive one. By reading the chemical story told by CK-MB, LDH, and AST, medical teams could now:
Verify the success of the surgical procedure by comparing enzyme patterns to established norms.
Identify issues early, often before patients showed any outward signs of trouble.
Track the recovery process as enzyme levels returned to normal baseline values.
While modern technology has given us even more precise tools, like the protein Troponin, the fundamental principle remains the same. The courageous early work of tracking enzymes in pioneering heart-lung machine patients laid the foundation for the safe, monitored cardiac surgery that saves countless lives today. It taught us that even when the heart is silent, it never stops communicating.